1. Field of the Invention
This invention relates to a device for feeding a web, and more particularly to an improvement in a web feeding device employing rubber rollers as feed rollers.
2. Description of the Prior Art
In a web feeding device for feeding a photographic film like a microfilm, there have been used rubber rollers. The rubber rollers are advantageous as compared with metal rollers in that they have much less friction, smaller inertia and soft surface and accordingly they can be driven by a motor of small torque and will not damage the surface of the film. Therefore, the rubber rollers have been desired as the feed rollers for feeding a roll film like a microfilm in a microfilm reader, a microfilm camera or the like.
As one of the microfilm recorders there has been known a computer output microfilmer (COM) which records the output of a computer directly on a microfilm. In the COM, there are two types of display system in one of which the output of a computer is once displayed on a CRT and the image on the CRT is optically focused on a microfilm for recording the image thereon, and in the other the output of the computer is directly recorded on a microfilm by a scanning laser beam modulated by the output signal from the computer which is called "laser com." In the COM, an X-Y direction driving mechanism is provided for moving the microfilm in the X and Y directions to carry each frame to the recording station. The X-Y direction driving mechanism is driven by a motor, which is heated during operation and warms the interior of the COM.
Further, there are photosensitive type recording film and a heat sensitive type recording film in the film to be used in the laser com. The heat sensitive film is able to be monitored simultaneously with recording. In the monitoring operation, it is necessary to illuminate the recorded part of the film. The illuminating device, however, further heats the interior of the COM.
When the sequential temperature fluctuation in the apparatus is large as mentioned above due to the heating, the diameter of the rubber roller for feeding the microfilm is changed and accordingly the amount of film feed is changed. For example, when the rubber roller is made of urethane rubber (specific gravity: 1.27, hardness: 80) having a diameter of 23 mm, the fluctuation for the amount of film feed of 150 mm is about 0.03 mm/C..degree. since the linear expansion coefficient is 2.times.10.sup.-4 /C..degree. (20.degree. C.-100.degree. C.). Therefore, when the temperature within the apparatus rises 40.degree. C., there appears an error of 1.2 mm.
The above error in the amount of film feed is serious particularly in case of COM (148.+-..sup.0 1.0 in the standard of National Micrographics Association). In the conventional apparatus, however, the error in the amount of film feed due to the sequential temperature varation has not been corrected.